Process for removing mercaptans from mineral oils



W( H. RUPP Nov. 4, '1952 PROCESS FOR REMOVING MERCAPTANS FROM MINERAL,OILS

Filed Aug. 16. 195o U :.m DSU .E/ mam i doku/ZOU I |20 m4mm wl/ll#Patented Nov. 4, 1952 i PROCESS FOR REMOVING MERCPTAN S FROM MINERALOILS Walter. H. Rupp, Mountainside, N. VJ assigner to `Standard OilDevelopment Company, a corporation of Delaware Application August 16,1950, Serial No. 179,812

6 Claims. 1

The present invention is concerned with the refining of mineral oils andis more particularly concerned with the removal of mercaptan compoundsfrom naphthas from catalytic cracking.

Naphthas obtained by the catalytic cracking of hydrocarbons containunstable aromatic mercaptans and dioleflns which react to formundesirable gums and resins when the naphtha is exposed to air orprolonged heating.

It is known to remove these mercaptans by treatment with caustic soda.However, the naphtha fractions so treated often contain considerablequantities of hydrogen sulfide and carbon dioxide with the result thatcaustic consumption is excessive. In order to avoid excessive causticconsumption it has been proposed to separate a well fractionated lightside stream from the catalytic naphtha, strip it to specificationboiling point and wash this cut with caustic. This process, however, hasthe disadvantage that the absence of the heavy naphtha increases gasproduction by reducing the mols of liquid in equilibrium with the gasesvented from the top of the boiling between about 250v and about 400 F.containing 1-5% of the hydrogen sulfide. The rough cut vnaphtha containsthe aromatic mercaptans boiling about 300 F. and higher. This is cooledand washed with .01 to 0.2 volume of caustic per, volume of rough cutnaphtha, preferably in a' countercurrent contacter, at 80-150 F. Thecontactor is of conventional type having either perforated plates,packing or other contacting devices. The washed naphtha is then injectedinto the overhead condenser inlet line and re` mixed with the lightnaphtha and gas fractions.

By so doing, the low pressure gas volume is held to a minimum and isunchanged'from normal operating procedures.

For a further understanding of the invention,

reference may be had to the accompanying drawing in which the singlefigure is an elevational view, generally diagrammatic, showing anapparatus embodying the improvement of the presenty invention.

Referring now to this drawing, the total effluent from a catalyticcracking reaction zone is introduced by line l to the lower part offractionating zone 2 when it is subjected to the usual distillation andfractionating processing to give a light overhead, and naphtha and gasoil side cuts.

According to the present invention, all fractions boiling below 250 F.and taken overhead through line 3, and condensed in condenser 4. Theliquid and gas from condenser 4 are passed to separator 5 from which lowpressure gas is removed through line 6 and low pressure distillatethrough line 1. A further feature of the invention involves the removalof a rough fraction boiling from about 250 F. up to abouti/00 F.7throughline 8. This fraction is cooled in cooler 9 and a portion thereof may bereturned as reflux through line I0. The remainder of this fraction ispassed to contacting zone Il where it is passed countercurrent to acaustic soda solution of 5% to 20% strength introduced through line [3at a temperature between and 150 F. A treat of 1-'5% of caustic byvolume on naphtha usually suffices for removing the aromatic mercaptans.In this operation the caustic removes the troublesome aromaticmercaptans from the roughly fractionated naphtha. Since most of the gasand acidic components have been removed from this fraction the causticrequirements are materially lowered. The washed naphtha is then passedby line l2 to condenser 4 where it ismixed with the overhead condensate.By operating in this manner the heavy naphtha is recombined with the gasand acts to dissolve large portions of it in the low pressure distillatethus avoiding overloading the low pressure compressors in subsequentprocessing. The spent caustic is removed from contactor I l through lineI4 and passed to the sewer or to mercaptan recovery units.

The nature and objects of the present invention having been thusdescribed and illustrated, what is claimedA as new and useful and isdesired to be secured by Letters Patent is:

1. Process for treating a catalytically cracked mixture of hydrocarbonsboiling in the naphtha range which comprises fractionally distillingsaid mixture to form an overhead vapor fraction boiling up to about 250F., removing a second fraction boiling in the range of about 250 F. to400 F., caustic washing said second fraction, combining the overheadvapor and the caustic washed fraction, thereafter condensing at least aportion of the said vapor fraction while in admixture and contact withthe said caustic washed fraction.

2. Process as described in claim 1 in which the side stream fraction iscaustic washed with between .01 and 0.2 volume of caustic per volume ofside stream.

3. Process as described in claim 1 in which the y 3 side stream iscaustic treated at a temperature between about 80 F. and 150 F.

4. Process for removing mercaptans from the products of a catalyticcracking operation which comprises fractionally distilling said productsin a distillation column to form various boiling range fractions;removing. a rst fraction boilingup to about 250 overhead as a vapor,removing a second fraction boiling roughly between 250 F.

combining the overhead vapor and the caustic washed fraction, thereaftercondensing at least a portion of the said vapor fraction While in admixture and contact with the said caustic washed fraction.

5. Process as in claim 4 intwhich a part of the' cooled side stream isreturned to the distillation column as reux.

4 6. Process as in claim 4 in which the cooled side stream is causticwashed with between .01 and 0.2 volume of caustic per volume of sidestream at a temperature between 80 F. and 150 F.

WALTER H. RUPP.

REFERENCES CITED.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,827,537 Morrell Oct. 13, 19312,070,295 Morrell Feb. 9, 1937 2,090,007 MacKenzie Aug. 17, 19372,297,537 Craig et al. Sept. 29, 1942 2,343,927 Hellman July 20, 1943

1. PROCESS FOR TREATING A CATALYTICALLY CRACKED MIXTURE OF HYDROCARBONSBOILING IN THE NAPHTHA RANGE WHICH COMPRISES FRACTIONALLY DISTILLINGSAID MIXTURE TO FORM AN OVERHEAD VAPOR FRACTION BOILING UP TO ABOUT 250*F., REMOVING A SECOND FRACTION BOILING IN THE RANGE OF ABOUT 250* F. TO400* F., CAUSTIC WASHING SAID SECOND FRACTION, COMBINING THE OVERHEADVAPOR AND THE CAUSTIC WASHED FRACTION, THEREAFTER CONDENSING AT LEAST APORITON OF